1. Relay ladder diagrams: we love them, we love them not;Krigman;InTech,1985
2. J.T. Welch and T.E. Nelson, “Synchronous PLC relay ladder logic”, submitted for publication.
3. An old favorite gets new standards;Gayman;Manu. Eng.,1988
4. Programmable Logic Controllers, Architecture and Application;Michel,1990
5. Ladder diagram and sequential function chart languages in programmable controllers;Wareham;Can. Mach. Metalwork.,1988